The human baby is born extremely immature, with its major organs and immune system not fully developed. for its survival, the infant depends on an extraordinarily well-adapted evolutionary strategy shared by all mammals: breastfeeding. But what does milk contain that makes it so essential for the newborn and how does it provide immunity, nutrition, and a source for optimal growth? Human milk is a very complex living fluid which comprises proteins, carbohydrates, lipids, cells and other biologically important components. These milk components interact synergistically with each other and their environment (the infant's gut) at a biomolecular level with the final result being that breastmilk feeds and protects the newborn. This article summarises the key characteristics of breastmilk proteins and describes their functions as critical molecules conferring human milk with its diverse bioactive properties. Also presented are some of the factors which hav an influence on the quantity and quality of breastmilk proteins.